The present invention relates to a method for controlling a piston fed wood grinder, wherein a plurality of wood charges are fed by pressure medium driven pistons against stones for grinding.
Previously the work of a piston fed wood grinder has been controlled by maintaining the feed pressure of the pistons or the feed power of the pistons at a constant value or by maintaining the control valve of the feed pressure in a constant position. These earlier methods have the common advantage of being realizable in a simple manner. On the other hand they have the common serious draw-back that due to unevenness in the quality of the wood to be ground the rate of movement of the piston will vary, wherefore the pulp produced will not be of uniform quality. The importance of uniform quality of the pulp, again, has in recent times steadily grown.
Although this problem had been recognized a long time ago, no satisfactory solution has been found by means of which the rate of movement of the piston would be maintained essentially constant; one reason for this being that the feed piston moves very slowly and speed changes which may be absolutely small in toto relatively great have been difficult to observe and to compensate for.
It is the object of the present invention to provide a new control method which overcomes the afore mentioned difficulties.